Question

A man sitting in a train travelling at the rate of 50 km/hr observes that it takes 9 sec for a goods train travelling in the opposite direction to pass him. If the goods train is 187.5 m long, find its speed ?

Answer 1

Let the speed of the goods train be x km/hr. 

Relative speed = (50 + \(x\)) km/hr

= (50 + \(x\)) x \(\frac{5}{18}\) m/s

∴ \(\frac{187.5}{(50\,+x)\times\frac{5}{18}}\) = 9 ⇒ \(\frac{187.5\times18}{250+5x}\)

⇒ 250 + 5\(x\) = 187.5 × 2 = 375 

⇒ 5\(x\) = 375 – 250 = 125 

⇒ \(x\) = 25 km/hr.